This proposal describes research into the physicochemical properties of selected plasma proteins including antithrombin III, Cl-inactivator, alpha2-plasmin inhibitor, and fibronectin, all of which have potential value for replacement therapy in patients with either inherited or acquired deficiences. The program will expedite the development of new or improved methods of isolating and preserving these proteins in a form suitable for clinical evaluation. The solubility of various proteins will be evaluated in the presence of polyethylene glycol, an inert fractional precipitating agent, which is being developed as an alternative to ethanol for large-scale fractionation. We will seek ways of selectively manipulating the solubility of specific proteins, for example by addition of substances with which they preferentially interact. Secondly, these proteins will be examined with respect to their stability towards various forms of stress, with particular emphasis on thermal stability, the objective being to define conditions under which they can be pasteurized to diminish the risk of transfusion hepatitis. Finally, we propose to develop a broad program of investigation of protein-protein and protein-ligand interactions in human plasma, with emphasis on the use of fluorescence spectroscopy and high pressure liquid chromatography. Systems to be investigated include: (1) the interaction of the above three protease inhibitors with the relevant proteases and zymogens, (2) the interaction of fibronectin with fibrin(ogen), collagen, and heparin, (3) the interaction between various fragments of these proteins. The results of these studies, in addition to clarifying structure/function relationships, will be applied to the development of fluorescent binding assays and improved purification schemes based on affinity principles.